1. Field of the Invention
The present invention relates to a target device and a light detecting device for receiving a light beam such as a laser beam or the like which is applied thereto and detecting the position where the light beam is applied.
2. Description of the Related Art
Target shooting sports including gun shooting, Japanese archery, archery, etc. have heretofore gained popularity among many people. At present, not only Japanese archery and archery, but also gun shooting are played in competitions. According to a typical gun shooting competition, a player shoots a bullet from an air rifle or a laser beam from a laser gun toward a target, and competes for a higher score based on the accuracy with which the bullet or the laser beam hits the target.
FIG. 1 of the accompanying drawings shows partly in block form a conventional gun shooting competition system for shooting a target with a laser beam emitted from a laser gun. As shown in FIG. 1, the conventional gun shooting competition system has laser gun 120 operated by a shooter for shooting laser beam 130, target device 110 for detecting a shot impact position where laser beam 130 shot from laser gun 120 hits target plate 140 mounted on target device 110, display unit 191 for displaying the information as to the shot impact on target device 110, and switching unit 192 interconnecting target device 110 and display unit 191. Laser gun 120 and target device 110 are spaced from each other by a predetermined distance for shooting competitions. Switching unit 192 comprises a switching hub of 10BASE-T LAN (Local Area Network) 193.
A processing sequence of the conventional gun shooting competition system at the time the shooter shoots laser beam 130 from laser gun 120 will be described below.
When the shooter operates laser gun 120 to shoot laser beam 130 by triggering laser gun 120 while directing laser gun 120 toward target device 110, laser beam 130 is shot from laser gun 120. Laser beam 130 shot from laser gun 120 is typically emitted from a semiconductor laser oscillation device mounted in laser gun 120.
As with a real bullet shot from a real gun, laser beam 130 is shot from the muzzle of laser gun 120 and travels straight in the direction in which laser gun 120 is oriented.
When laser beam 130 shot from laser gun 120 hits target plate 140 mounted on target device 110, target device 110 detects the shot impact position on target plate 140, and transmits information representing the detected shot impact position via switching unit 192 to display unit 191.
Display unit 191 calculates a score of the shot based on the shot impact position information transmitted from target device 110, and displays the calculated score. Display unit 191 has registered therein information for identifying the shooter, e.g., the identification number of the shooter, and information representing the present shot number of the laser beam shot by the shooter. Therefore, display unit 191 also displays the identification number of the shooter, the present laser beam number, the score corresponding to the laser beam number, the total score gained thus far, and the shot impact position of laser beam 130 on target plate 140, either simultaneously or at spaced time intervals.
As shown in FIG. 2 of the accompanying drawings, target plate 140 has on its surface ten annular areas, including a central circular area just around center O, divided by ten concentric circles around center O. These areas are also referred to as score areas. Target plate 140 also has an outside area around the annular areas. The shooter gets no score when laser beam 130 hits the outside area. A score for the outermost annular area, i.e., the annular area marked with “1”, is 1. Scores for the other annular areas are progressively incremented by 1 toward center O, and the score for the central circular area is 10. A score which the shooter obtains when shooting target plate 140 is determined based on the distance from center O of target plate 140 to the impact position on target plate 140.
As shown in FIG. 3 of the accompanying drawings, target device 110 has optical filter 117 comprising a bandpass filter for receiving laser beam 130 which has been shot from laser gun 120 and hit target plate 140 and passing only a light beam which has the wavelength of laser beam 130 shot from laser gun 120, PSD (Position Sensitive Detector) sensor 111 for detecting the laser beam emitted from laser gun 120 and transmitted through optical filter 117 and generating a current based on the amount of the detected light beam and the shot impact position of laser beam 130 on target plate 140 mounted on target device 110, amplifier 113a for amplifying a signal represented by the current generated by PSD sensor 111 and outputting the amplified signal, sample-and-hold circuit 118 for sampling the signal from amplifier 113a at given time intervals and outputting the sampled signal, A/D converter 115 for converting the signal output from sample-and-hold circuit 118 into a digital signal and outputting the digital signal, photodiode sensor 112 for generating a current based on an amount of extraneous light applied to target device 110, an amplifier 113b for amplifying a signal represented by the current generated by photodiode sensor 112 and outputting the amplified signal, a subtractor 114 for subtracting the signal output from amplifier 113b from the signal output from amplifier 113a and outputting a differential signal, and impact position calculator 116 for calculating the shot impact position of laser beam 130 on target plate 140 and detecting a shot impact position detecting signal for identifying laser beam 130, which is contained in laser beam 130 shot from laser gun 120, based on the signal output from subtractor 114.
Operation of target device 110 thus constructed will be described below.
When laser beam 130 shot from laser gun 120 hits target plate 140 mounted on target device 110, laser beam 130 is applied to optical filter 117 in target device 110 and only a light beam having the wavelength of laser beam 130 shot from laser gun 120 is transmitted through optical filter 117 and detected by PSD sensor 111.
PSD sensor 111 generates currents based on the amount of the light beam received through optical filter 117 and the impact position of laser beam 130 on target plate 140. PSD sensor 111 has a two-dimensional current generating membrane for generating a current based on the detected light beam. If the light beam received through optical filter 117 is applied as a beam spot to the two-dimensional current generating membrane at a coordinate position (x, y), then the two-dimensional current generating membrane generates therein currents which are two-dimensionally linearly commensurate with the coordinate position (x, y). Specifically, the two-dimensional current generating membrane generates two currents Ix1, Ix2 flowing in two opposite directions along the x-axis and two currents Iy1, Iy2 flowing in two opposite directions along the y-axis.
PSD sensor 111 outputs a signal based on the currents Ix1, Ix2 flowing along the x-axis and a signal based on the currents Iy1, Iy2 flowing along the y-axis. Actually, since PSD sensor 111 also detects extraneous light which has the wavelength laser beam 130 and which has passed through optical filter 117, the signals output from PSD sensor 111 contain currents generated by the extraneous light applied to target device 110 and transmitted through optical filter 117, added to the currents along the x-axis and the currents along the y-axis. PSD sensor 111 outputs the sum of the currents along the x-axis and the currents along the y-axis as a signal representing the amount Σ of light received through optical filter 117.
The signal output from PSD sensor 111 is amplified by amplifier 113a, which outputs the amplified signal.
As shown in FIG. 4a of the accompanying drawings, the amplified signal output from amplifier 113a has a waveform including waveform component 101 based on laser beam 130 shot from laser gun 120 and waveform component 102a based on the extraneous light which is applied to target device 110 and transmitted through optical filter 117 and detected by PSD sensor 111.
Photodiode sensor 112 generates a current based on only the extraneous light which is applied to target device 110. A signal represented by the generated current is amplified by amplifier 113b, which outputs the amplified signal.
As shown in FIG. 4b of the accompanying drawings, the amplified signal output from amplifier 113b has a waveform including only waveform component 102b based on the extraneous light which is applied to target device 110.
The signal output from amplifier 113a is supplied to sample-and-hold circuit 118. Sample-and-hold circuit 118 samples the signal based on laser beam 130 shot from laser gun 120, of the signal output from amplifier 113a, at such a time that laser beam 130 is applied to target device 110. Thus, sample-and-hold circuit 118 detects a change in laser beam 130, and outputs a signal representing the detected change in laser beam 130. In this manner, the signal component representing the extraneous light that has the wavelength of laser beam 130 and has passed through optical filter 117 is removed from the signal output from amplifier 113a, and hence only the signal based on laser beam 130 shot from laser gun 120 is extracted.
The signal output from sample-and-hold circuit 118 is converted by A/D converter 115 into a digital signal that is applied to impact position calculator 116.
Subtractor 114 subtracts the signal output from amplifier 113b as shown in FIG. 4b from the signal output from amplifier 113a as shown in FIG. 4a, thus extracting the signal based on only laser beam 130 shot from laser gun 120 as shown in FIG. 4c of the accompanying drawings. The signal extracted by subtractor 114 as shown in FIG. 4c is supplied to impact position calculator 116.
Impact position calculator 116 detects a shot impact position detecting signal contained in laser beam 130 shot from laser gun 120 based on the signal output from subtractor 114, and calculates a shot impact position of laser beam 130 on target plate 140 based on the digital signal output from A/D converter 115.
Specifically, when the signal output from subtractor 114 is supplied to impact position calculator 116, impact position calculator 116 converts the current value of the signal representing the amount Σ of light, of the signal output from subtractor 114, into a voltage value, and detects a shot impact position detecting signal for identifying laser beam 130, which is contained in laser beam 130 shot from laser gun 120, depending on the voltage value.
When laser gun 120 shoots laser beam 130, it also outputs a shot impact position detecting signal having a predetermined period and amount of light in order to identify laser beam 130 as being shot from laser gun 120. When impact position calculator 116 detects the shot impact position detecting signal contained in laser beam 130 shot from laser gun 120, using the voltage value of the signal representing the amount Σ of light, of the signal output from subtractor 114, the laser beam detected by target device 110 is identified as being shot from laser gun 120.
When the signal output from A/D converter 115 is supplied to impact position calculator 116, impact position calculator 116 calculates a shot impact position of laser beam 130 on target plate 140, using the current values Ix1, Ix2, Iy1, Iy2 which are generated depending on the shot impact position of laser beam 130, according to the following equations:x=k(Ix2−Ix1)/(Ix2+Ix1)  (1)y=k(Iy2−Iy1)/(Iy2+Iy1)  (2)
The beam spot position where both (Ix2−Ix1), (Iy2−Iy1) are zero is defined as the electrical and mechanical coordinate origin (0, 0) of PSD sensor 111. Target plate 140 needs to be positioned two-dimensionally with respect to PSD sensor 111 within an allowable accuracy range.
Inasmuch as the impact position (x, y) calculated according to the above equations is affected by the amount Σ of light due to the characteristics of PSD sensor 111, impact position calculator 116 thereafter divides the value of the impact position (x, y) by the signal representing the amount Σ of light, thus correcting the shot impact position of laser beam 130 on target plate 140.
With target device 110 shown in FIGS. 1 and 3, as described above, the extraneous light having wavelengths different from the wavelength of laser beam 130 shot from laser gun 120 is removed by optical filter 117, and a change in laser beam 130 shot from laser gun 120 is detected. Thus, the signal based on only laser beam 130 shot from laser gun 120 is detected, and the shot impact position of laser beam 130 on target plate 140 is detected based on the signal thus detected. The extraneous light having the wavelength of laser beam 130 shot from laser gun 120 is removed by subtracting the extraneous light detected by photodiode sensor from the light transmitted through optical filter 117, thus detecting the shot impact position detecting signal contained in laser beam 130 shot from laser gun 120. In this fashion, the shot impact position of laser beam 130 on target plate 140 is detected without noise and error.
In order to detect the shot impact position of the laser beam shot from the laser gun on the target plate without noise and error, the extraneous light having wavelengths different from the wavelength of the laser beam shot from the laser gun is removed by the optical filter, and thereafter a change in the laser beam shot from the laser gun is detected. Thus, the signal based on only the laser beam shot from the laser gun is detected, and the shot impact position of the laser beam on the target plate is detected based on the signal thus detected. The extraneous light having the wavelength of the laser beam shot from the laser gun is removed by subtracting the extraneous light detected by photodiode sensor from the light transmitted through optical filter, thus detecting the shot impact position detecting signal contained in the laser beam shot from the laser gun. However, since the optical filter used to remove the extraneous light having wavelengths different from the wavelength of the laser beam shot from the laser gun is expensive, the manufacturing cost of the conventional gun shooting competition system is increased simply by using the optical filter, and hence it is difficult to reduce the manufacturing cost of the conventional gun shooting competition system.